Preparation of rare refractory metal powders by electrolysis



Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE FRANK H; DRI GGS, OF BLOOMFIELD, NEW J EBSEY, ASSIGN OR TO .WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA PREPARATION OF RARE REFRACTORY METAL POWDERS BY ELECTROLYSIS INo' Drawing.

This invention relates to the art of metallurgy and more particularly to the art of preparing the so-called rare refractory metals and comprises essentially in a method of preparing these metals in the pure powder state by the electrolysis of their fused salts.

This invention is an improvement of the methods set forth in copending applications Serial No. 275,204, filed May 4:, 1928, issued as Patent 1,815,054 on July 21, 1931 and entitled Method of producing tantalum, and application Serial N 0. 277,096 filed May 11,

1928, issued as Patent 1,842,254 on J anuary r ing tantalum metal powder by the electrolytic dissociation of an alkali double fluoride compound in solution in a fused bath comprised of alkali fluorides to which is added a proportion of an oxygen carrying compound of tantalum.

The process disclosed by the above identified copending application Serial No. 277,096

is specifically directed to a method of preparlng uranium by the electrolytic decomposition of a fused bath comprised of fused.

' alkali metal fluorides containing a proper? tion of a double alkali metal fluoride compound such as KUF The process disclosed by the above identified application Serial No. 309,682 is specifically directed to the preparation of chromium by the electrolytic decomposition of a fused bath comprised of calcium chloride to which have been added a proportion of chromium oxide (Gr o with or without the addition of a proportion of an alkali chromium halogen compound.

In the application of these general methods to the production of rare refractory metal powders it has been found that the Application filed November 1, 1928. Serial No. 316,624.

usual particle size of the metal powder so produced is sufliciently small so that the bulk of it will readily pass a 250 mesh screen and a great part of it will pass 400 to 500 mesh screen. This fine particle size renders it diflicut to wash the metal powder free of the accompanying water soluble salts in a short interval of time and without deleterious reaction with the aqueous and acid solution during the prolonged settling periods. In the more reactive metals such as uranium and thorium, a fine particle size is highly undesirable, due to the danger of spontaneous combustion upon exposure of the dry powder to the atmosphere. In lesser reactive metals, such as tantalum, chromium, etc., the time interval involved in the recovery of such a fine metal powder from the fusion mixture is highly-undesirable. In addition thereto, the subsequent degasification of a rare refractory metal powder prior to sintering according to the method set forth and described in copending application Serial No. 717,490, filed June 5, 1924, issued as Patent 1,814,719 on July 14, 1931 entitled Ductile thorium, etc., and assigned to the same assignee as the present invention, is rendered exceedingly difii'b' cult and tedious with decrease in particle size of the metal powder.

It is inexpedient from a commercial production standpoint to effect an increase in particle size of the rare refractory metal powder by raising the temperature of the bath during the electrolysis reaction and it is also inexpedient to effect an increase in the particle size of the metal powder by means of localizing the heat energy liberated at the cathode by means of concentrating the current density to a relatively small area by reducing the size of said cathode. Because of the relatively high chemical activity of the rare metals it is essential to keep both the temperature of the bath and the local heat energy at the cathodeas low as practical, preferably below 1000 C.

It is therefore'one of the objects of this invention to provide a means of increasing the particle size of the rare metal powder without materially effecting an increase in the temperature of the fused bath.

Another object of the present invention is to provide a means of controlling the particle size of refractory metal powders prepared by the electrolytic dissociation of their compounds in fused baths.

Another object of this invention is to provide a-means of rendering said rare refractory metal powders more coarsely uniform in size.

Another object of this invention is to provide an additive component to the fluoride fusion bath which will effectively increase the particle size of the rare refractory metal powder without materially raising the fusion point of the bath and which will be non-contaminating with respect to said rare refractory metal powder.

Otherobjects and advantages will become apparent as the invention is more fully disclosed.

In accordance with my invention I have determined that a proportion of an ionized chloride compound in the fusion mixture comprised of alkali fluorides and alkali-rare metal double fluorides with or Without the accompanying oxygen carrying compound as set forth in application Serial No. 275,264 and Serial No. 277,096,0r the addition of a proportion of a rare metal chloride, an alkali metal chloride or a double alkali metal-rare metal chloride compound to the alkali earth metal chloride fusion of application Serial No. 309,682 materially effects the particle size of the resultant rare refractory metal powder.

The specific reaction involved which produces this 'marked effect in the particle size of the metal powder is at present unknown and no theories so far advanced adequately explains the observed phenomena. Whatever the theory involved or the true reaction taking place, I have found that the addition of relatively small amounts of such an ionizable chloride compound causes a pronounced alteration and increase in the particle size and uniformity of particle size of the rare refractory metal powder.

Whereas I have specifically determined that any ionizable chloride compound will suffice for the purpose of increasing the particle size of the rare refractory metal owder, for the purpose of maintaining a high standard of purity in the metal powder product I must employ those chloride compounds which are non-reactive or non-con- I taminating with respect thereto, and pref- 'erably employ those chloride compounds which are water or acid soluble. For best results I have determined that alkali metal chlorides or a'lkali-rare metal double chloride compounds are the most desirable compounds to employ for the purpose of this V invention although other chloride compounds may be equally as desirable.

In the application of this invention in the ride compound to cause a decided coarsening in the resultant metal powder. This is due to the fact that after the lixiviation or washing procedure to free the rare metal powder of the water and acid soluble salts of the fusion mixture, a certain amount of insoluble oxide, basic fluoride and flake carbon or graphite will be found remaining which must be removed by settling or gravity separation methods. In order to accomplish this most conveniently the major portion of the metal powder must be relatively coarse. As heretofore stated, relatively small amounts of ionized chloride compounds markedly effect the particle size of the metal powder, and increased amounts of said chloride ion increases this effect.

In applying this invention to increase the particle size of tantalum produced by the electrolytic dissociation of the double fluoride compound as by the method disclosed in application Serial No. 275,264 I prefer to employ the alkali metal chlorides, either singly or admixed in various proportions.

The specific fusion mixture I prefer to employ contains the following:

compound employed.

1 part Although the above fusion mixture specifically discloses potassium chloride as the compound employedto give the chloride ion to the fusion, it is not to be construed thereby that I am limited to the use of this compound as I may employ any other alkali chloride or a proportion of alkali metaltantalum double chloride compound or I may add any other non-contaminating non-deleterious chloride compound which substantially will produce the same result.

When the fusion mixture has been brought to a quiet fusion it may be electrolyzed under practically the same temperature conditions heretofore disclosed in the above identified copending application Serial No. 275,264.

The resulting metal powder product will be found to differ materially from the metal powder product of a non-chloride containing fusion in that the particle size thereof instead of passing readily through a 250 mesh screen will that is approximately thereof will be retained. Of the metal powder passing 30 mesh, the largest bulk will be retained on the 60 mesh screen and only about 10% of the total weight will pass 100 to 200 mesh.

This material increase in particle size is "be substantially retained on a 20 mesh screen,

particularly useful in subsequent washing and gravity separation methods and enables me to obtain moreeasily a final product which is substantially free from the deleterious oxide, basic fluoride and flake carbon and carbide compounds heretofore encountered in metal powders prepared by a non-chloride containing fusion.

In addition thereto, the Subsequent heat treating procedures which require substantial degasification of the rare metal powder prior to actual sintering thereof is rendered more efficient and rapid by the relatively large particle'size of the metal powder product.

While the specific embodiment of this invention has disclosed the application or use of the ionized chlorine as a component of the tantalum fluoride fusion, the method or invention may be equally as well applied to the other refractory metals prepared by analogous methods.

By the addition of alkali metal chlorides to the method disclosed in application Serial No. 277,096 I have been enabled thereby to materially increase the particle size of the uranium metal powder. By the addition to the fusion disclosed in application Serial No. 309,682 of an ionizable chlorine compound such as the 3KCLCrCl compound the s ecific electrolysis ofchromium oxide (c 6 wasthereby facilitated and the particle size of the metal powder materially increased.

By the addition of a proportion of an alkali chloride to the alkaline earth metal chloride flux such as disclosed in application Serial No. 309,682 I am substantially enabled to effect a material increase and coarsening of uranium metal powder prepared thereby. The particular fusion mixture I prefer to employ is approximately equal molecular weights CaCl and NaCl, to which mixture I add preferably the oxide free double fluoride compound KUF It is apparent therefore that there may be many variations and applications made of the process disclosed in the specific embodiment without substantially departing from the nature of my invention as described in the following claims.

What is claimed is:

1. In the preparation of rare refractory metal powders by electrolytic dissociation of their fused salts, the method of increasing the particle size thereof comprising adding to the fused bath a proportion of an ionizable chloride compound substantially nonreactive with the rare refractory metal.

2. In the preparation of rare refractory metal powders by the electrolytic dissociation of a fused bath comprised in part of an ionized salt of said refractory metal, the method of increasing the particle size thereof comprising adding to the fusion mixture a proportion of an ionizable chloride compound substantially nonreactive with the rare refractory metal.

3. In the preparation of rare refractory metal powders by the electrolytic dissociation of a fused bath comprised substantially of fused alkali fluorides containing a proportion of an ionized rare refractory metal compound, the method of increasing the particle size of said rare refractory metal powder which comprises adding to the fusion mixture a proportion of an ionizable chloride compound substantially non-reactive with the rare refractory metal.

4. In the preparation of rare refractory metal powders by the electrolytic dissociation of a fused bath comprised substantially of fused alkaline earth metal halides containing a proportion of an ionized rare refractory metal compound, the method of effecting an increase in the particle size of said rare refractory metal which comprises adding to the fusion mixture a proportion of an ionizable chloride compound substantially nonreactive with the rare refractory metal.

5. In the preparation of tantalum by the electrolytic dissociation of a fusion mixture comprised of alkaline fluorides, alkali fluotantalates and an oxygen containing compound of tantalum, the method of increasing the particle size of the said tantalum metal powder which comprises adding to the said fusion mixture a proportion of an alkali metal chloride.

6. In the preparation of tantalum metal powder by the electrolytic dissociation of a fused fluoride bath comprised in part of an ionized tantalum compound, the method of increasing the particle size of said tantalum metal powder which comprises adding to the fusion mixture a proportion of an alkali metal chloride.

7. In the preparation of rare refractory metal powders by the electrolytic dissociation of a fused bath containing a proportion of an ionized rare refractory meta-l compound, the method of increasing the particle size of said rare refractory met-a1 powder without materially increasing the temperature of said bath which comprises adding thereto a proportion of alkali metal chlorides.

8. In the preparation of rare refractory metal powders by electrolytic dissociation of fused compounds thereof, the method of effecting an increase in the particle size of said metal .powders while maintaining the temperature of said bath below 1000 C. which comprises adding thereto a proportion of alkali metal chlorides. r

9. In the preparation of rare refractory metal powders by the electrolytic dissociation of fused baths comprised in part of an ionized rare refractory metal compound, the method of increasing the particle size of said metal powder without increasing the localized cathode heat energy which comprises adding to said fusion mixture a proportion of alkali metal chlorides.

5 10. The method of preparing rare refractory metal powders which comprises electrolytlcally decomposing a fusion mixture comprised of an alkali metal fluoride compound, an alkali metal chloride compound, and a proportion of a double alkali metal-rare refractory metal halide compound.

11. The method of preparing tantalum metal powder which comprises electrolytical- 1y decomposing a fusion mixture comprised of alkali metal fluoride compound, an alkali metal chloride compound, a proportion of a double alkali metal-tantalum halide compound and a proportion of an oxygen containing tantalum compound.

12. The method of preparing tantalum metal powder which comprises electrolytically decomposing a fused bath comprised of potassium fluoride and potassium chloride to p which has been added a proportion of potassium tantalum fluoride and a proportion of an oxygen containing compound of tantalum. 1

13. The method of preparing tantalum metal powder which comprises electrolytical- 1y decomposing a fusion mixture comprised of about 1 part potassium fluoride, about 2 parts potassium chloride, about 1 part potassium fluotantalate and a proportion of tantalum oxide.

14. In the preparation of tantalum by the electrolytic dissociation of a fusion mixture comprised of alkaline fluorides, alkali fluotantalates and an oxygen containing com-. pound of tantalum, the method of increasing the particle size of the said tantalum metal powder which comprises adding to said fusion mixture a proportion of potassium chloride. In testimony whereof, I have hereunto subc5 scribed my name this th day of October,

' FRANK H. DRIGrGrS.v 3 

